The present invention relates to the packaging of integrated circuits (ICs) and more particularly to coating the leads of a lead frame to prevent contamination of the leads during the die attach process.
In many types of semiconductor packages, especially those for high power devices, an integrated circuit die is attached to a die pad of a lead frame with solder paste and then pads on the die are electrically connected to lead fingers of the lead frame with wires. The solder paste is used in order to enhance reliability and thermal conductivity. However, when the die is attached to the die pad, some flux may be deposited on the lead fingers, such as during a reflow operation, causing the formation of tin clouds on the lead fingers. The flux and tin clouds can compromise the subsequent bond between the wire and the lead fingers, leading to bonds that don't stick or a bond with a low peel strength.
It would be advantageous to be able to attach a die to a lead frame with solder paste but not compromise the integrity of subsequent wire bonds to the lead fingers of the lead frame.